Why do people fall in love and end up CRYING?

It is a big question for me of why do people fall in love and hurt afterwards. why is that? it makes me think crazy because its not good to be hurt. for me i don't like to be hurt, i don't like crying because it is a sign of weakness and self pity, i understand that it hurt when you fail for a certain thing but when it comes to LOVE i really don't get it.